Cartilage tissue can be found throughout the human anatomy. The cells within cartilage tissue are called chondrocytes. These cells generate proteins, such as collagen, proteoglycan, and elastin, that are involved in the formation and maintenance of the cartilage. Hyaline cartilage is present on certain bone surfaces, where it is commonly referred to as articular cartilage. Articular cartilage contains significant amounts of collagen (about two-thirds of the dry weight of articular cartilage), and cross-linking of the collagen imparts a high material strength and firmness to the tissue. These mechanical properties are important to the proper performance of the articular cartilage within the body.
Articular cartilage is not vascularized, and when damaged as a result of trauma or degenerative causes, this tissue has little or no capacity for in vivo self-repair. A variety of therapeutic solutions have been proposed for the treatment and repair of damaged or degenerated cartilage. Tissue healing involves cell migration that redistributes cells from the surrounding tissues to the injury site. In cartilage tissue, however, the ability of chondrocytes to migrate from their native lacunae site may be very limited due to the supposed rigidity of the matrix. To compensate for the migration deficiency, various surgical interventions for cartilage repair focus on delivering reparative cells or tissues. For example, marrow stimulation attempts to tap marrow cells by breaching the subchondral bone, although the mechanical durability of resultant fibrocartilage is often unsatisfactory. Autologous chondrocyte implantation (ACI) directly establishes a chondrocyte presence in the treatment site through the delivery of culture-expanded chondrocytes. Despite being associated with some measure of clinical success, ACI is associated with technical hurdles such as the cell culture preparation, two-stage surgical procedure, and challenging procedural aspects to place small pieces of cartilage into the defect sites.